HP OpenVMS Systems Documentation

HP TCP/IP Services for OpenVMSGuide to IPv6

An anycast address is an identifier for a set of interfaces typically
belonging to different nodes. Packets sent to an anycast address are
delivered to one of the interfaces identified as the
"nearest" address, according to the routing protocol's
measure of distance.

Anycast addresses are allocated from the unicast address space, and
cannot be distinguished from unicast addresses. Only the subnet-router
anycase address and addresses defined in RFC 2526 are easily
identified. Packets sent to the subnet-router anycast address are
delivered to the router closest to the originating host only.
Figure 1-9 shows the format of anycast addresses.

In the stateless model, nodes learn address prefixes by listening for
Router Advertisement packets. Addresses are formed by combining the
prefix with a data link-specific interface token, which is typically
derived from the data link address of the interface. This model is
favored by administrators who do not need tight control over address
configuration. See RFC 2462 for more information.

In DHCPv6, hosts may request addresses, configuration information and
services from dedicated configuration servers. This model is favored by
administrators who want to delegate addresses based on a client/server
model.

Note

This version of TCP/IP Services for OpenVMS does not support DHCPv6.

In both cases, the resulting addresses have associated lifetimes, and
systems must be able to acquire new addresses and release expired
addresses. Combined with the ability to register updated address
information with Domain Name System (DNS) servers, these mechanisms
provide a path towards network renumbering and provide network
administrators with control over the use of network addresses without
manual intervention on each host on the network.

The Domain Name System (DNS) provides support for mapping names to IP
addresses and mapping IP addresses back to their corresponding names.
Because of the increased size of the IPv6
address, the DNS has the following new features:

AAAA resource record type This holds IPv6 addresses, encoded in
network byte order. The version of BIND shipped with TCP/IP Services
for OpenVMS supports AAAA records.

AAAA query
A query for a specified domain name in the Internet class returns
all associated AAAA resource records in the response.

IP6.ARPA domain for looking up a name for a specified address
(address-to-name mapping) An IPv6 address is represented in reverse
order as a sequence of 4-bit nibbles separated by dots with the suffix
.IP6.ARPA appended. For example, the IPv6 address
4321:0:1:2:3:4:567:89ab
has the following reverse lookup domain name:

IPv6 addresses are now being deployed by the regional registries. See
the IANA web page at the following location for more information:

http://www.iana.org

In addition, you can contact your Internet Service Provider (ISP) to
obtain an IPv6 address.

Because of the need to test various implementations of the IPv6 RFCs,
the IETF has defined a temporary IPv6 address allocation scheme. You
can assign the addresses in this scheme to hosts and routers for
testing IPv6 on the 6bone (a prototype IPv6 implementation that can be
used for testing). See the 6bone home page at the following location
for more information about 6bone address allocation and assignment:

Because the Internet and most likely your network are based on IPv4,
you need to know how to use this routing infrastructure to carry your
IPv6 traffic while you gradually build up your IPv6 routing
infrastructure. The best mechanism to employ for routing IPv6 traffic
across IPv4 routing infrastructures is tunneling. The following types
of tunnels are supported:

Automatic

6to4

Configured

The following sections describe each tunnel and its advantages and
disadvantages. The more powerful the tunnel, the more configuration and
administration it requires.

An IPv6 automatic tunnel is the simplest tunnel to configure and
deploy. This mechanism enables hosts with a globally unique IPv4
address to automatically create a tunnel over an IPv4 network. The
tunnel is created as a virtual interface (TN0) and is configured with
an IPv4-compatible IPv6 address, which is derived from the IPv4
address. The destination address of the packet determines the tunnel
destination endpoint. See Section 1.2.2.1 for more information about
IPv4-compatible IPv6 addresses.

This mechanism is good for introducing hosts to IPv6 because it permits
application porting, testing, and experimentation with the IPv6
protocol. However, an automatic tunnel has the following limitations:

Requires a globally unique (not private) IPv4 address.

Benefits hosts more than routers. You can neither run the RIPng
protocol over the automatic tunnel nor can you forward packets over the
tunnel.

Communicates only with other nodes that are configured with
IPv4-compatible IPv6 addresses. You cannot communicate with nodes that
are configured with native IPv6 addresses only.

Is quite possibly going to be deprecated by the IPv6 community.
Therefore, do not deploy this in your production environment.

A 6to4 tunnel is a type of automatic tunnel, but it offers greater
connectivity. This mechanism enables a special IPv6 site, called a 6to4
site, with a single, globally unique IPv4 address to automatically
create a tunnel over an IPv4 network to communicate with other 6to4
sites. The tunnel is created as a virtual interface (TNn) on a node at
the IPv4 network attachment point. This node is either an individual
host or a router called a border router. The tunnel is configured with
a special 6to4 address that is derived from the IPv4 address. The
destination address of the packet determines the tunnel destination
endpoint.

Within the 6to4 site, the border router creates the 6to4 site prefix
from its globally unique IPv4 address and advertises the prefix to all
nodes in the 6to4 site. Each node automatically configures its 6to4
address based on the 6to4 prefix; no special configuration is
necessary. Nodes within the 6to4 site communicate with each other using
native IPv6. Any traffic that is addressed outside the site is
forwarded to the border router.

This mechanism is easy to configure and can be deployed in a production
environment. However, a 6to4 tunnel has the following limitations:

Communicates only with other nodes that are configured with 6to4
addresses. However, if you use third-party 6to4 Relay Router services
or 6to4 relay services on the Internet, you can communicate with nodes
that are configured with native IPv6 addresses only.

Relies on the underlying IPv4 network routing infrastructure.
Therefore, routing might not be as efficient as native IPv6
connectivity or configured tunnels.

A configured tunnel is the most complex tunnel to configure and deploy.
There are two types of configured tunnels:

IPv4 configured tunnel---encapsulates IPv4 or IPv6 packets in an
IPv4 packet and carries those packets through an IPv4 network
infrastructure. An IPv6 over IPv4 configured tunnel enables IPv6 sites
and hosts to communicate with other IPv6 nodes across an IPv4 network.

IPv6 configured tunnel---encapsulates IPv4 or IPv6 packets in an IPv6
packet and carries those packets through an IPv6 network
infrastructure. An IPv6 over IPv6 configured tunnel is an enabling
technology for mobile IPv6, and can also be used for traffic
engineering (for example, IPv6 multihoming support).

A configured tunnel is created as a virtual interface (ITn) and uses
IPv4 addresses (IPv4 configured tunnel) or IPv6 addresses (IPv6
configured tunnel) as the source and destination endpoints. If you want
to send IPv6 traffic through any configured tunnel, you configure an
IPv6 address on the tunnel interface. If you want to send IPv4 traffic
through any configured tunnel, you configure an IPv4 address on the
tunnel interface.

This mechanism is the most powerful tunneling mechanism, but has the
following limitations:

Requires a coordinated configuration of each tunnel endpoint.

Relies on the expertise of the administrator to obtain efficient
routing of traffic. If the endpoint is misconfigured, you might have
inefficient routes, routing loops, or both.

This section shows some example IPv6 configurations. Select a
configuration that most closely matches the environment in which you
want to configure IPv6 on your system.

Figure 1-11 shows a simple LAN configuration in which host A and host
B communicate using IPv6 with no router.

Figure 1-11 Host-to-Host Configuration with No Router

Figure 1-12 shows a simple LAN configuration in which host A, host B,
and router A communicate using IPv6. Host A and host B obtain global
addresses from router A.

Figure 1-12 Host-to-Host Configuration with Router

Figure 1-13 shows a configuration in which two IPv6 networks are
connected through an IPv6 router (router A).

Figure 1-13 IPv6 Network to IPv6 Network with Router
Configuration

Figure 1-14 shows a configuration in which four IPv6 networks are
connected using three routers. The three routers exchange routing
information with each other using the RIPng protocol.

Figure 1-14 Multiple IPv6 Networks and Multiple Routers
Configuration

Figure 1-15 shows a configuration in which host A and host B,
connected to an IPv4 network, communicate using IPv6 through an IPv4
tunnel.

Figure 1-15 Host-to-Host Configuration over Tunnel

Figure 1-16 shows a configuration in which host X is connected to an
IPv4 network. Router A, an IPv6 router, is connected to the same IPv4
network and is also connected to two IPv6 networks. Host X communicates
with host B using IPv6 through an IPv4 tunnel between host X and router
A.

Figure 1-16 Host-to-Router Configuration over Tunnel

Figure 1-17 shows a configuration in which four IPv6 networks are
connected through two routers and an IPv4 network. Host A communicates
with host F through an IPv4 tunnel between router A and router B.

Figure 1-17 IPv6 Network-to-IPv6 Network Configuration over
Tunnel

Figure 1-18 shows a configuration in which host E is connected to an
IPv4 network. Router B, an IPv6 router, is connected to the same IPv4
network and also is connected to two IPv6 networks. Host E communicates
with host B using a 6to4 tunnel between host E and router B.